U.S. Pat. No. 3,645,049 (incorporated herein by reference) describes a flap wheel assembly of a type commonly used to abrade surfaces which includes a hub including means for affording attachment of the hub to a source of power to rotate the hub in a first direction about an axis. The hub has a plurality of similarly shaped slots which extend generally longitudinally of the hub, are spaced about its axis and open through the periphery of the hub. Each of the slots is generally keyhole-shaped in cross section, having a narrow portion adjacent the hub's periphery, and an enlarged inner portion spaced from the hub's periphery by its narrow portion. Also included in the flap wheel assembly are a plurality of tablet-like abrasive packets each comprising a plurality of pieces of abrasive-coated sheet material disposed face-to-back with first edges generally aligned to provide one major abrasive-coated face for the abrasive packet. A sheet of tough flexible attachment material has end portions projecting between the pieces from their first edges and fastened between the pieces by means adjacent the first edges that fasten the pieces of abrasive-coated sheet material together. A generally U-shaped bight portion of the sheet of attaching material for each abrasive packet projects from the first edges of its pieces of abrasive-coated sheet material, is inserted in a different one of the slots of the hub, and has a rod within its part in the inner portion of the slot to attach the abrasive packet to the hub.
While the flap wheel assembly described in U.S. Pat. No. 3,645,049 is quite serviceable for abrading outer planar or convex surfaces, the abrasive packets are closely spaced about the periphery of the hub so that they project generally radially of the hub and the sheets of abrasive-coated sheet material in each pocket have aligned outer edges which results in abrading action being provided only by narrow outer edge portions of the pieces of abrasive-coated sheet material in each abrasive packet.
Less closely spaced packets have been used around the periphery of a similar hub to allow the abrasive-coated face of the packet to have more surface contact with surfaces being abraded. This approach, however, has still not provided the long scratch pattern that is often desired when surfaces are being abraded.
Also the flap wheel assembly has a relatively large diameter that limits its usefulness for abrading the inner surfaces of small tubes.